1. Field of the Invention
This invention relates to a signaling system for a connection oriented packet network, and more particularly to a high speed connection setup/release signaling system.
2. Description of the Related Art
Conventionally, the controling procedure of connection setup/release between a source terminal and a destination terminal on a connection oriented packet network, that is, a signaling system, is constituted in order to accommodate a connection oriented terminal of a low function such as the telephone set. Accordingly, a large number of complex signaling messages to be communicated is complicated to process. Consequently, such a signaling system is not suitable for a high speed connection setup. When a connectionless terminal such as a computer is accommodated while using the signaling procedure as is, the connection setup delay time causes a serious problem in applications requiring a fast response.
A complicated controlling procedure is disclosed in "Draft Text for Q.93B", pp. 1-72, which is a draft for standardization from the Working Party XI/6 in Study Group XI of CCITT held in Geneva June 22 to 26, 1992.
In the draft for standardization, it is determined that signaling is performed by the exchange of messages, including six messages including SETUP for establishing connection, three messages including Disconnect for cancelling connection, and three messages including Status as other messages. The structure of the messages includes common portions including a protocol identifier, a call number and a type of message, and special information factors for the individual messages.
In the conventional signaling system, since a virtual channel (VC) is setup and released each time an application, packet transmission or burst transmission is started and ended, when an application is started and ended frequently like an interactive connectionless packet, the time required to connect and disconnect the VC becomes longer than the time during which data are transferred. In particular in the communication of a packet to the same destination, the VC to the same destination must be setup/released frequently.
Information factors of the setup message for establishing connection in Q.93B employ, in order to designate the called party to be connected, a traffic descriptor for a signal bandwidth, necessary for communication using a called party number and a called party subaddress. Since each exchange can only perform signaling for a hop-by-hop routing wherein it examines the called party number and the traffic descriptor in a received setup message to determine a certain next route having a necessary signal bandwidth and performs, after arriving at the object of the called party address, signaling with the called party subaddress, when a plurality of stages of switches are involved, much time is required for processing of routing selection at each of the switching systems. Consequently, there is a drawback in that the end-to-end VC setup time is long.
Further, in Q.93B, since a terminal performs, when it is in a connection setup phase, acquisition of a VC for transmission and acquisition of an end-to-end communication route by way of communication of the six messages including Setup, the processing delay time and the propagation delay time cannot be ignored even when a small amount of data is communicated.
Accordingly, in order to achieve setup signaling quickly, instead of a countermeasure wherein a VC is allocated on demand by the switching system for each transmission of a packet, signaling wherein the terminal itself has some VCI(VC Identifier) initially and can select a VC without interaction with the switching system is required.